This became a pretty big topic on the beta forums during the different beta phases. The devs have stated that this was a conscious decision and that the music was in fact composed in a way that would make it hard to have it constantly playing. I think the idea was that the music has more impact if it suddenly start playing when traversing an area after it only being ambient sounds for a while or something like that. The devs seemed completely against allowing for it to be constantly played at first but after a pretty big number of players in the betas raised this topic the dev feedback notes after beta phase 3 said that they would seriously look into this issue again and see if they could make changes. I do not know where to find this post now that the beta forums are closed unfortunately. As for the mount-music getting old, it can be turned off in System Config./Sound Settings.